NFL Officiating – question…

Question for readers – seeking an answer: do we know for sure that each of the officials calling a particular game does not have any particular allegiance to one of the 2 teams on the field. I don’t have time to look this up, but I wonder if the NFL has a system in place to avoid this potential issue. Do they have some sort of jury-selection-like process to try to weed out any potential bias? For example, I didn’t feel it was necessarily fair that Mike Ditka was allowed to ref the last Packers/Bears game. Further, I wonder how it would work if I went into NFL officiating. Right now anyway, I would be unable to objectively ref the Packers or Buffalo (due to positive bias) or the Bears, Vikings, Eagles, Cowboys, New England, NYG or Seattle (due to their collective lameness). Seriously.